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Batless

Bats have tiny bones. The radius, or forearm bone, of Myotis lucifugus, commonly known as the little brown bat, is about an inch and a half long. Its circumference is not much greater than that of a pine needle. At Aeolus Cave, in Vermont, the ground is littered with bat bones. There are so many of them—thousands upon thousands—that you can’t take a step without crunching them underfoot.

The other day, Ryan Smith and Joel Flewelling, of the Vermont Fish and Wildlife Department, were standing on some bat bones in Aeolus, gazing at the ceiling. They were accompanied by Susi von Oettingen, a biologist with the Fish and Wildlife Service; David McDevitt, a representative of the Nature Conservancy, which owns the cave; and Sebastian Frank, who is Smith’s brother-in-law. Frank was filming the trip for a local public-access TV channel. He said he didn’t know when the film would air, but he promised that it would be “long and arty.”

Smith and Flewelling were running a bat census. When they found a cluster hanging from the ceiling, they would count each bat and call out its species. By the light of her headlamp, von Oettingen would record the results.

“Two lucis,” Smith said, using the shorthand for Myotis lucifugus.

“Two lucis,” von Oettingen repeated, writing the number down on an index card.

Set into a mountainside in the town of Dorset, Aeolus Cave used to be the largest bat hibernaculum in New England. As recently as 2007, it was estimated that almost three hundred thousand bats over-wintered there. Then white-nose syndrome, the fungal disease that has laid waste to bat populations all across the Northeast, swept through. By the winter of 2009, the population in the cave was plummeting so fast that Vermont officials began to wonder if, by the end of the season, there would be any bats left. They arranged to send corpses from Aeolus to the American Museum of Natural History, so that at least there would be a record of the animals’ genetic makeup.

Smith and the rest of the group continued to work their way deeper into the cave. Many of the bats hanging from the ceiling were dead, their toes still hooked to the rock. They were dry and shrivelled, like little mummies. Smith skipped those in his count. Von Oettingen gestured toward a crack in the rockface. Apparently, at one point, there had been dozens of bats hibernating inside it. Now there was a layer of black muck studded with toothpick-size bones. She recalled seeing, on an earlier visit to the cave, a live bat trying to nuzzle a group of dead ones. “They’re very social, you know,” she said. “It just broke my heart.”

Since white nose was first discovered in a cave near Albany, New York, three years ago, it has spread to ten other states. In that time, the fungus has acquired a scientific name, Geomyces destructans, and has been shown to be related to another fungus, Geomyces pannorum, which causes skin infections in humans. It seems that bats can pick up white nose from other bats, and also from the environment. But a great deal about the fungus remains unclear. It is not known where it came from, or exactly how it kills bats, or even for sure whether it does. (White nose could be an opportunistic infection that is a symptom of some other disease.) Nor has anyone come up with a way to combat it. In many hibernacula—the disease seems to afflict bats only during the winter—the mortality rate has reached over ninety per cent. It is believed that white nose, or whatever white nose is a sign of, has wiped out at least a million bats, and probably many more.

Aeolus Cave has one main chamber, which is tall enough for a human to stand up in. In an average winter, it used to shelter three thousand hibernating bats, and the count took an hour. This time, the census was finished in twenty minutes.

“Let’s head out,” Smith said when he reached the chamber’s back wall.

“That’s it?” von Oettingen asked.

“That’s it,” Smith replied.

“There really is nothing else to count,” von Oettingen agreed. She tallied up the figures: eighty-eight Myotis lucifugus; one Myotis septentrionalis, commonly known as a northern long-eared bat; three Perimyotis subflavus, or tricolored bats; and twenty bats of indeterminate species. The total came to a hundred and twelve.

“That’s one-thirtieth of what we should have seen,” she said. “You just can’t keep up with that kind of mortality.”

Everyone filed out of the cave, over the tiny bones. ♦

Elizabeth Kolbert has been a staff writer at The New Yorker since 1999. She won the 2015 Pulitzer Prize for general nonfiction for “The Sixth Extinction: An Unnatural History.”